This invention relates to machines for assisting in connecting a series of pipe stands to or disconnecting them from the upper end of a string of well pipe.
When it becomes necessary during the drilling of a well to remove the entire drill string from the well, in order to replace a bit at the lower end of the string or for other reasons, the various stands which make up the string are sequentially detached from the upper end of the string and temporarily stored in a rack in a side of the derrick. After the bit has been replaced or another desired operation has been performed, the stands are sequentially removed from the rack and returned into the hole. This round trip procedure requires the presence of several men on the rig floor for making and breaking connections and moving the pipe stands, and also requires a derrickman at an elevated location in the rig for controlling the pipe at that location and moving the upper ends of the pipe stands into and out of the racking board. In addition to the expense involved, the round tripping procedure is dangerous to all of the men on the rig, and very time consuming. There have been attempts in the past to mechanize some of the steps involved in handling the pipe during a round trip, but none of these prior expedients has to my knowledge proven effective or practical enough for any wide scale adoption in the actual drilling of wells.